IBM builds nanotube light emitter

Yorktown Heights, N.Y. - IBM Corp. researchers have discovered that simultaneously injecting electrons into one end of a carbon nanotube and holes into the other yields a device that can emit light at the 1.5-micron wavelength. IBM Research here has thus effectively produced the world's smallest solid-state emitter.

Unlike light-emitting diodes, which emit light whenever a voltage appears across their two terminals, the three-terminal light-emitting nanotube (LEN) device uses the nanotube as the channel of a transistor. As a result, the electrons and holes are poised to flow into the source and drain, with the third terminal, the gate, turning the current on and off.

"We have advanced our understanding of the electrical properties of nanotubes to emit light, thereby accelerating the development of electronic and optical applications," said Phaedon Avouris, manager of nanoscale science at IBM Research.

IBM emphasized that these are re-search results. However, researchers of-fered a detailed mathematical proof along with verifying laboratory demonstrations of hitherto speculative properties of light emission by carbon nanotubes.

Arrays of LENs will do more than convert electricity into light, Avouris said. Because they are transistors, they can be used to process information-for example, storing the pixel values for a nanoscale display. IBM also released a detailed characterization of the LENs' light-emitting properties, calling the nanotube-based material "uniquely one-dimensional." That is because nanotubes can be microns long but are only 1.4 nm in diameter, inviting the mathematical approximation of one-dimensionality.

Last year, Avouris employed carbon nanotubes to create the "world's best transistor." IBM characterized both n-type and p-type FETs, fabricated with conventional MOSFET processing technology, using carbon nanotubes as the channel. And two years ago, IBM developed a bulk process by which it manufactures nanotubes. The bulk process has produced nanotube transistors only 10 atoms wide, or 500 times smaller than current silicon transistors.

The nanotube transistors were enabled by an innovative patented process that IBM has dubbed "constructive destruction." It destroys defective nanotubes right on a wafer, rather than requiring that good ones be painstakingly constructed one by one, as other research labs now do.